Synthesis of Lateral Macrobicyclic Compartmental Ligands: Structural, Magnetic, Electrochemical, and Catalytic Studies of Mono- and Binuclear Copper(II) Complexes

• Published in: Inorganic chemistry Vol. 42; no. 10; pp. 3308 - 3317
• Main Authors: Thirumavalavan, M, Akilan, P, Kandaswamy, M, Chinnakali, Kandaswamy, Kumar, G. Senthil, Fun, H. K
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 19.05.2003
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic020633+

A series of putative mono- and binuclear copper(II) complexes, of general formulas [CuL](ClO4) and [Cu2L](ClO4)2, respectively, have been synthesized from lateral macrocyclic ligands that have different compartments, originated from their corresponding precursor compounds (PC-1, 3,4:9,10-dibenzo-1,12-[N,N‘-bis{(3-formyl-2-hydroxy-5-methyl)benzyl}diaza]-5,8-dioxacyclotetradecane; and PC-2, 3,4:9,10-dibenzo-1,12-[N,N‘-bis{(3-formyl-2-hydroxy-5-methyl)benzyl}diaza]-5,8-dioxacyclopentadecane). The precursor compound PC-1 crystallized in the triclinic system with space group P1̄. The mononuclear copper(II) complex [CuL1a](ClO4) is crystallized in the monoclinic system with space group P21/c. The binuclear copper(II) complex [Cu2L2c](ClO4)2 is crystallized in the triclinic system with space group P1̄; the two Cu ions have two different geometries. Electrochemical studies evidenced that one quasi-reversible reduction wave (E pc = −0.78 to −0.87 V) for mononuclear complexes and two quasi-reversible one-electron-transfer reduction waves (E 1 pc = −0.83 to −0.92 V, E 2 pc = −1.07 to −1.38 V) for binuclear complexes are obtained in the cathodic region. Room-temperature magnetic-moment studies convey the presence of antiferromagnetic coupling in binuclear complexes [μeff = (1.45−1.55)μB], which is also suggested from the broad ESR spectra with g = 2.10−2.11, whereas mononuclear complexes show hyperfine splitting in ESR spectra and they have magnetic-moment values that are similar to the spin-only value [μeff = (1.69−1.72)μB]. Variable-temperature magnetic susceptibility study of the complex shows that the observed −2J value for the binuclear complex [Cu2L1b](ClO4)2 is 214 cm-1. The observed initial rate-constant values of catechol oxidation, using complexes as catalysts, range from 4.89 × 10-3 to 5.32 × 10-2 min-1 and the values are found to be higher for binuclear complexes than for the corresponding mononuclear complexes.